1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device including a module assembly.
2. Discussion of the Related Art
In general, flat panel display devices are thin, light weight, and have low power consumption, thus their application in portable devices is increasing. Among the various types of flat panel display devices, liquid crystal display (LCD) devices are widely used for laptop computers and desktop monitors because of their superiority in resolution, color image display, and display quality.
LCD devices make use of a optical anisotropy and polarization properties of liquid crystal molecules to generate a desired image. In particular, liquid crystal molecules can be aligned in a specific orientation by controlling the application of an electric field across the liquid crystal molecules. Due to the optical anisotropy, incident light is refracted according to the orientation of the liquid crystal molecules, thereby generating the desired image.
Specifically, an LCD device includes upper and lower substrates with electrodes formed thereon, wherein the substrates are disposed to be spaced apart and facing each other with a liquid crystal material interposed therebetween. When a voltage is applied to the electrodes to generate an electric field across the liquid crystal material, an alignment direction of the liquid crystal molecules changes in accordance with the applied voltage. As a result, light transmittance through the liquid crystal material varies and images are formed.
Most LCDs are passive devices, in which images are displayed on the liquid crystal panel by controlling the amount of light input from an outside light source. Thus, a separate light source (i.e., backlight device) is generally employed to irradiate an LCD device.
FIG. 1 is a schematic cross-sectional view of a liquid crystal display module according to the related art. In FIG. 1, a liquid crystal display module (LCM) includes a liquid crystal panel 2, a main support 14, a top case 10, a bottom case 50, and a backlight unit. The liquid crystal panel 2 comprises a lower substrate, an upper substrate and a liquid crystal layer interposed between. The main support 14 supports the liquid crystal panel 2, and the top case 10 surrounds the edges of the liquid crystal panel 2 and the main support 14 therein. The backlight unit is consisting of a plurality of optical sheets 32, 34, and 36, and a light guide plate 24. Furthermore, a lamp 20 and a lamp housing 16 are equipped within the backlight unit. The bottom case 50 supports and accommodates the backlight unit with coupling to the top case 10.
On outer surfaces of the liquid crystal panel 2, an upper polarizer 42 is provided to attach onto top of the liquid crystal panel 2, and a lower polarizer 40 is provided to attach onto the bottom of the liquid crystal panel 2. Although not shown, a plurality of pixels are disposed in the liquid crystal panel 2 having a matrix configuration, wherein each pixel includes a thin film transistor (TFT) to drive the liquid crystal molecules.
In FIG. 1, the top case 10 has an L-shaped cross section, and covers the side and the top portions of the main support 14 and the edge portion of the liquid crystal panel 2. Although not shown, the top case 10 may be coupled with the main support 14 by a plurality of screws. The main support 14 is generally formed by a molding die process. When the main support 14 is formed of a metal, for example aluminum (Al), the main support 14 exhibits superior thermal conductivity for a high resolution television and/or computer monitor. The main support 14 includes a protrusion 14a that extends from a body of the main support 14 and supports the liquid crystal panel 2.
The backlight unit is disposed underneath the protrusion 14a and the main support 14. The backlight unit includes a lamp 20 emitting light, a lamp housing 16 accommodating the lamp 20, a light guide plate 24 guiding the incident light toward the liquid crystal panel 2, a reflector 26 disposed underneath the light guide plate 24 and reflecting the light toward the liquid crystal panel 2, a light diffusing sheet 32 disposed on the light guide plate 24, a first prism sheet 34 disposed on the light diffusing sheet 32, and a second prism sheet 36 disposing on the first prism sheet 34. The lamp 20 is a cold cathode fluorescent lamp (CCFL), and the lamp housing 16 accommodates and surrounds the lamp 20 to protect and hold it in place. Furthermore, the lamp housing 16 has an opening along one side and reflects the light to lead the light toward the light guide plate 24.
The light guide plate 24 has a front surface facing the diffusing sheet 32 and a back surface facing the reflector 26. The front surface is a horizontal plane to output the light, and the back surface is formed of an incline surface so that the light from the lamp 20 is converted into surface light by the light guide plate 24. The reflector 26 is arranged underneath the light guide plate 24 and upwardly reflects the light to reduce light loss and increase light efficiency. When the light from the lamp 20 is incident to the light guide plate 24, the back surface having the incline plane uniformly reflects the incident light toward the front surface of the light guide plate 24. In addition, some portions of the light from lamp 20 are upwardly reflected by the reflector 26 toward the light guide plate 24. The light diffusing sheet 32 diffuses the light received from the light guide plate 24 in order to improve the brightness and to increase the range of vision.
Meanwhile, the light perpendicularly enters the liquid crystal panel 2 in order to increase light efficiency. Therefore, two prism sheets 34 and 36 are used to direct the light to be perpendicular to the liquid crystal panel 2. Specifically, the light emitted from the lamp 20 is perpendicularly incident to the liquid crystal panel 2 by way of passing through the light guide plate 24 and the prism sheets 34 and 36.
However, the above-mentioned liquid crystal module (LCM) has some problems. When the LCM having the aforementioned structure is operated for an extended period of time, the lamp 20 may emit significant amounts of heat. Therefore, the emitted heat may cause creation of wrinkles in the light diffusing sheet 32 and the prism sheets 34 and 36. Furthermore, the wrinkles can cause the deterioration of the displayed-image, such as wrinkled images. Especially, since the main frame 14 has the protrusion 14a that can restrict lateral movement as well as vertical movement provided for the optical sheets 32, 34, and 36, the wrinkle phenomenon becomes worse in the optical sheets 32, 34, and 36.